For most families, especially for those with children in the family, a bath tub is required for the reason that conventional baths in rest rooms are always too large for a child. In addition, because a bath tub normally has very large volume, it will take up large space for placement. When the bath tub is not in use, it's hard for users to find space for placing the bath tub. For this reason, there are some kinds of foldable bath tubs in the market at present. For example, these foldable bath tubs generally comprise a foldable supporting frame and a main body made of flexible material. In these cases, the main body is supported by the foldable supporting frame. Such bath tubs have a large number of elements, thus being inconvenient for operating when folded and unfolded. Furthermore, a fold line based on which the folding or unfolding is performed can be easily worn, causing water leakage in these worn places.